The study aimed to assess the proliferative activity and karyotype in Oral Lichen Planus (OLP) lesions. G-banding chromosomal analysis of short-term primary cultures, and immunohistochemical expression of Ki67 and p53 were applied in 30 consecutive OLP patients divided into two groups according to clinical presentation of the lesions, and in nine subjects as negative controls. Mean values of Ki67 and p53 expression differed significantly (P<.01) between controls and patients groups with reticular or atrophic-erosive forms of OLP, whereas there was no significant difference between the two groups of patients with reticular or atrophic-erosive lesions. Six OLP patients showed clonal chromosome alterations, four of them associated with p53 overexpression. In conclusion, OLP is characterized by a high cellular turnover in most patients irrespective of clinical disease presentation. The genetic instability found in some patients should be interpreted as a consequence of the enhanced epithelial turnover, although we cannot rule out the possibility that some of the cytogenetic non-random anomalies observed represent early steps in cancer development.